Touring the Interface with a Basic Composite - Nuke 101: Professional Compositing and Visual Effects - page 65

You need to define the path you're going to write to, the name of the file, and
the type of file you're going to write to disk. The plan is to create a folder in
yourNuke101foldercalledstudent_filesandrenderaTIFFimagesequencethere
called doll_v01.
2. In the Write1 Properties panel, look at the File property line. At the far right
there's an icon of a folder (the top one, the bottom one belongs to something else
called Proxy). Click it ( FIGURE 2.33 ) .
Figure 2.33. It's small, so make sure this is what you are clicking.